The correct answer is c) head.
The head of a bone is a smooth, rounded structure that typically articulates with another bone at a joint. It is often found at the proximal end of long bones, such as the femur or humerus, and fits neatly into a socket or cavity of another bone, allowing for smooth movement. While terms like crest, ridge, condyle, and trochlea describe other bone features, the term ‘head’ specifically refers to this rounded articular surface.